Self-Assembly of Nanoparticles at Solid and Liquid Surfaces

Abstract

The research field of nanoparticle synthesis and related nanoparticle applied sciences have been steadily growing in the past two decades. The chemical synthesis of nanoparticles was improved up to the point that the organic and inorganic nanoparticle colloids are produced with a low size dispersion and with a well defined nanoparticle shape in large quantities. A stunning feature of a drying nanoparticle colloidal solution is the ability to create selfassembled arrays of nanoparticles. The self-assembled nanoparticle arrays mimic the natural crystals. The size of perfectly ordered domains is limited by the size dispersion of nanoparticles. Consequently the defects in the self-assembled structure are obvious and unavoidable. Despite these defects, the self-assembled nanoparticle arrays represent a new class of nanostructures built on “bottom-up” technological approach to fabrication. The traditional way of “top-down” fabrication technology primarily based on nano-lithography is complex, including many technological steps, time consuming and expensive. The main advantage is the tight control of all parameters governing the final nanostructures. On the other hand, the emerging fabrication technologies based on the self-assembled nanoparticles are fast, less complex and more price competitive. An extensive research is now focused on a deeper understanding of processes that control the self-assembly. New routes for directed or stimulated self-assembly are studied to achieve a tighter control than readily available in the spontaneous self-assembly. In this chapter we will discuss the spontaneous nanoparticle self-assembly with emphasis on characterization of nanoparticle arrays at various stages of the self-assembly process. The main diagnostic technique used throughout this chapter will be the grazing-incidence small-angle X-ray scattering (GISAXS) that represents a reliable and simple monitor of nanoparticle arrangement. The theoretical background of GISAXS and required instrumentation are described in Section 2. The most flexible surface to study the nanoparticle self-assembly processes is the liquid surface. The Section 3. reviews the latest results of studies combing the GISAXS technique with Langmuir nanoparticle layers on the water subphase. Almost all relevant nanoparticle applications rely on self-assembled arrays on solid surfaces. The Section 4 describes in detail the possibilities of nanoparticle transfer from liquid onto solid surfaces. The post-processing of self-assembled nanoparticle arrays and their applications are reviewed in the last Section 5.